The present invention relates to a focused ion beam apparatus.
A focused ion beam apparatus is used in a variety of applications, such as micropatterning, observation and analysis of semiconductor devices or the like, correcting defects of photomasks, preparation of TEM samples. A liquid metal ion source is widely used as an ion source in the focused ion beam apparatus, and gallium is generally used as an ion element.
With the use of the focused ion beam apparatus using a gallium liquid metal ion source, metal ions irradiated on a work surface of a sample to be worked remain as an impurity with respect to the sample after the metal ions finish the initial purpose, adversely affecting the sample. For example, a semiconductor device polluted with gallium causes an increase in leak current and suffers a shorter life, and a photomask polluted with gallium reduces the light transmittance.
As a solution to the problem, JP-A-2006-66398 proposes an ion source that does not affect a sample to be worked and includes a plasma chamber having an opening from which a plasma jet is extracted, and a reaction gas chamber provided in conjunction with the plasma chamber and having an opening for receiving a part of the plasma jet and an opening for extracting an active reaction gas.
Japanese Patent No. 3564717 proposes an ion source which draws ions by using the curvature of the equipotential surface of an ion sheath produced near the ion drawing opening.
The ion source described in JP-A-2006-66398 has the problem that the ion beam irradiated on a sample has energy spread due to the plasma potential generated and the beam size cannot be narrowed to disable observation or processing of micropatterns, as compared with an ion source using a liquid metal of gallium.
It is desirable that the current for generating an ion beam generated by a focused ion beam apparatus be set in a wide range of, for example, 10 pA or less to 10 nA or above and the ion beam be made narrower. The ion source therefore needs to draw ions with a high current density from a small area. However, the ion source described in Patent Document 2 suffers a somewhat limited range of the ion drawing current for the ion source is of a type which basically draws ions from the ion drawing opening whose radius is smaller than the thickness of the ion sheath of the plasma by using the curvature of the equipotential surface of the ion sheath. In addition, with a high current applied, it is difficult to narrow the beam size.
The present invention has been made in view of the foregoing situations, and it is an object of the invention to provide a focused ion beam apparatus which can make the beam size narrower and set the ion beam current variable in a wide range.